Deliverable	Due Date
Base Installation (nothing to submit)	Wednesday, February 4th at 1:00PM EST
Intro to Linux Gradescope Submission	Monday, February 9th at 1:00PM EST
Intro to Git Gradescope Submission	Monday, February 9th at 1:00PM EST

Intro to Linux

Table of Contents

• Introduction
• Gradescope Submission
• References
• Instructions
• Problems

Introduction

Linux is an essential part of the class, so it's important to get some experience with this before working with the robots. Although you're encouraged to collaborate with others if you are stuck, the lab should be completed individually so you can get practice with skills that will be essential later on in the course when you are in teams. If you have general questions, please post on Piazza so other students can benefit from the answer. If you have a question about your individual submission, please make a private post. Make sure you're using an Ubuntu terminal if you're testing the commands. Instructions for setting up the course software is here.

Gradescope Submission

Once you have completed the exercises below and filled in your linux_exercise.txt, you will submit a .zip file named lab1.zip containing your lab1 directory to Gradescope under Lab 1A: Intro To Linux. In Linux, the correct zip command is zip -r lab1 lab1. When you unzip lab1.zip, you should see a directory named lab1 containing a file named linux_exercise.txt.

References

If you don't have previous experience with Linux, we recommend that you read the following tutorials by the Software Carpentry Foundation before starting on the exercises. Otherwise, you can just use the resources as you need.

1. Setup
2. Introducing the Shell
3. Navigating files and directories
4. Working with files and directories
5. Pipes and filters
6. Finding things

Additionally, you may find the following IAP course useful: The Missing Semester of Your CS Education.

Instructions

1. Clone this repository by typing git clone https://github.com/mit-rss/intro_to_linux.git into your terminal. Please make sure you do this in ~/racecar_ws/src if you are using the Docker image.
2. Place your answers to problems 1-5 in linux_exercise.txt. Every command should go between the #####<question_number>####### and #####End of Question####### lines.
3. During this class, you will need to be familiar with at least one terminal-based text editor like vim, nano, or emacs. We recommend getting some practice with a terminal-based text editor when you're editing linux_exercise.txt.
4. Run sanity_checker.py to double check that your answers are correctly formatted.
5. Provide a single command for each of the following problems. If multiple answers are possible, choose the shortest answer. All of your commands should work regardless of your current working directory. Hint

Problems

Complete the following exercises inside your Docker container to access a Linux terminal.

Problem 1: Navigating your Home

The first thing you need to learn in the command-line is how to navigate the filesystem and view the contents of directories and files.

a. Navigate to your root directory.
b. Navigate to your home directory.
c. Navigate to the parent directory of your current directory.
d. Create a new directory ~/test.
e. List all the files/directories in your home directory, including hidden ones, in long listing format.
f. Print your current working directory.
g. Remove the new directory ~/test.
h. Display the contents of the file /etc/bash.bashrc.

Note: /etc/bash.bashrc is a system-wide file that is executed every time you open a new terminal. If you would like to add custom commands, please modify ~/.bashrc as done in problem 4, as changes outside the home directory are not saved on docker compose down.

Problem 2: Installing and Controlling Programs

One of the awesome features of UNIX-based operating systems is how simple it is to install programs through the terminal. For this problem, use the Advanced Packaging Tool or APT, which is the recommended way to install and manage Ubuntu packages.

a. Install a program called inxi.
b. Many commands display useful information when called with the help option. Enter a command to show the inxi help menu in the terminal to see what it does.
c. Additionally, there is a universally available reference bundled with almost every Unix system called "man pages" or manual pages. Enter a command to view the inxi man page for more detailed information.
d. Use inxi to show information about your hardware disk info.
e. Uninstall inxi.
f. Update the list of available Ubuntu packages.
g. Upgrade all existing packages.

Note: In APT, updating fetches the latest version of the package list, while upgrading upgrades the actual packages installed on your system. Before installing or upgrading, it is always a good idea to update the package list.

Problem 3: SSH

Another cool feature that you will be using often in this class is SSH (Secure SHell), which enables you to access the terminals of other Linux-powered remote devices or systems as long as you have access credentials. This is how you will access the racecars.

a. From your Docker container, log into a remote shell with the address athena.dialup.mit.edu and your kerberos as the username. This will give you secure remote access to a shell running on an Athena machine running Linux.
b. Logged into your Athena account, use wget to download the contents from https://tinyurl.com/ya67uga4 into a file named pic.png in your Athena home directory.
c. Exit the ssh session.
d. Using the scp command from your Docker container, move the photo you just downloaded from your Athena account, ~/pic.png, into the ~/racecar_ws directory in your Docker container. This is useful for transferring files between your computer and the racecar.

Problem 4: Tmux

In this class, you are going to be doing a lot of stuff in the terminal. A lot, a lot of stuff. Running multiple launch scripts, debugging, echoing ros2 topics, etc. Instead of having 15 tabs, where you have to run the same commands to initialize each and can only see one at a time, we can use something called a terminal multiplexer, or tmux. Tmux allows us to run multiple terminals, see them all on the same screen, and run commands to start each automatically. It can even allow us to run stuff in a terminal in the background, if we so desire. If we get super fancy, multiple people can attach to the same tmux session, and look at the same stuff at the same time.

a. Start a new tmux session named racecar from an existing terminal.

Now you should be in a tmux session! The following are some useful but by no means extensive set of commands to navigate inside a tmux session. Tmux uses Ctrl+b as the prefix key, meaning for the command Ctrl+b d, you press Ctrl+b, release Ctrl+b, then type d:

Command	Description
Ctrl+b %	Split pane vertically
Ctrl+b "	Split pane horizontally
Ctrl+b <arrow_key>	Switch between panes
Ctrl+b <Ctrl+arrow_key>	Change pane size
Ctrl+b c	Create new tab
Ctrl+b n	Switch between tabs

More commands can be found in this cheatsheet. Explore some tmux commands!

b. Detach from your current tmux session. This is similar to "saving and exiting" your tmux session.

When answering this question, you can use the corresponding tmux command or the keybinding. For the keybinding, enter in the following format: Ctrl+b <key>. For example, Ctrl+b c for creating a new tab.

c. List all active tmux sessions. You should see your racecar session!
d. Attach to the racecar tmux session.

You should now see that your previous racecar session is saved. Again, run the command to detach from your current tmux session.

e. Kill the racecar tmux session, ending all processes running in that session.
f. Enter a one-line command to add an alias tks for tmux kill-session to ~/.bashrc. Your ~/.bashrc file executes every time your new terminal opens, so you can now use the short command tks to kill your tmux session.

Hint: Use the echo and redirect (>>) commands.

Note: To be more exact, this command will work from the next time you open a new terminal. If you want to use the tks command in your current shell, you must run the command source ~/.bashrc, which executes the ~/.bashrc file in the current shell.

~/.bashrc is one of the many dotfiles. Dotfiles are configuration files that start with a dot (.), which makes them hidden by default. You cannot see them using the regular ls command; you need the -a flag (e.g., ls -a ~). These files customize your shell environment, editor settings, and various tools. For example, to configure your tmux keybindings, appearance, and behavior, you can create and modify the ~/.tmux.conf file.

g. Enter a one-line command to add the line set -g mouse on to your ~/.tmux.conf file. This allows you to click to select panes, resize windows, and scroll with your mouse wheel in tmux sessions.

Lastly, we can also use the tmuxp command to load tmux sessions from configuration files. We provide tmux_template.yaml which launches a tmux session named rss_tmux_template with multiple panes and tabs.

h. Load tmux_template.yaml using tmuxp.

Explore the tmux session. With your new alias and ~/.tmux.conf file, you should now be able to move between panes and tabs using your mouse and kill the tmux session by typing tks. You can explore other tmux configuration options here.

Problem 5: Environment Variables

Environment variables are dynamic values that affect the behavior of processes in your shell. They store configuration like your home directory ($HOME), executable search paths ($PATH), and application-specific settings such as $ROS_DISTRO.

a. Print the value of the HOME environment variable. This variable defines your home directory, ~.
b. Set the value of your HOME variable to /home/racecar/racecar_ws for the current session.
c. List all environment variables currently set in your shell. You should see your HOME variable set to /home/racecar/racecar_ws.

Try running cd ~ && pwd now. You should see that your home directory is now set to /home/racecar/racecar_ws. This is an example of how environment variables affect the behavior of your processes. For example, in ROS, running source /opt/ros/<ros_distro>/setup.bash sets up the required environment variables to have ROS properly functioning. More on this will be covered in Lab 1C.